In a conventional wireless communication system using a cellular systems, base stations transmit notification information at regular intervals within their own cells. The notification information mentioned here is various kinds of information that is used when a mobile terminal located in the cell performs wireless communication. For example, the notification information includes information on, for example, a cell ID for identifying a cell, paging period, and peripheral cells.
FIG. 17 is a schematic diagram illustrating an example of notification information transmitted by a conventional base station. As illustrated in FIG. 17, the notification information includes multiple system information blocks (SIB). In the example illustrated in FIG. 17, the notification information includes 11 SIBs: SIB1 to SIB11. Each of the SIB1 to SIB11 contain different information. For example, the SIB1 contains a “Value tag” that is incremented by a base station every time the notification information is updated. Furthermore, for example, the SIB2 contains information on a paging cycle. Furthermore, for example, the SIB3 contains a condition for moving to another cell. The remaining SIB4 to SIB11 also include various kinds of information related to the notification information.
In the example illustrated in FIG. 17, the base station transmits the notification information containing SIB1 to SIB11 at 720-ms intervals. When the power supply of the mobile terminal is turned on, when the mobile terminal moves between cells, when the notification information is changed, or when a predetermined time elapses, the mobile terminal receives notification information and stores therein the received notification information. Accordingly, wireless communication can be performed in the mobile terminal even when its power supply is being turned on or moving between cells.
Non Patent Literature 1: 3GPP TS 36.331 V9.1.0 (2009-12), “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification (Release 9)”
However, with the conventional technology, there is a problem in that electrical power consumed when a receiving process is performed on notification information increases. Such a problem will be specifically described using the example illustrated in FIGS. 18 and 19.
FIGS. 18 and 19 are schematic diagrams each illustrating an example of a transmission/receiving process performed by a conventional base station and a conventional mobile terminal on notification information. In the example illustrated in FIG. 18, it is assumed that a mobile terminal 92 is located in a cell formed by a base station 91. Furthermore, it is assumed that the power supply of the mobile terminal 92 is turned on and it is assumed that the mobile terminal 92 has already received the notification information from the base station 91 and is in a standby state.
As illustrated in FIG. 18, the base station 91 regularly transmits notification information containing the SIB1 to the SIB11. In this example, it is assumed that the information contained in the SIB2 is changed. In such a case, the base station 91 transmits paging in order to notify the mobile terminal 92 that the notification information has been changed. If the mobile terminal 92 receives the paging from the base station 91, the mobile terminal 92 confirms that the notification information has been changed and receives the notification information transmitted from the base station 91. At this time, the mobile terminal 92 receives all of the SIB1 to the SIB11 contained in the notification information and updates all the pieces of notification information retained in the mobile terminal 92.
In this way, if the mobile terminal 92 is notified that the notification information has been changed, the mobile terminal 92 receives all the pieces of notification information transmitted from the base station 91. Accordingly, as illustrated in the lower portion of FIG. 18, the mobile terminal 92 consumes received electrical power when it receives the SIB1 to the SIB11. Therefore, in the mobile terminal 92, electrical power consumed when the receiving process is performed on the notification information increases.
Furthermore, in the example illustrated in FIG. 19, it is assumed that, after the mobile terminal 92 moves from a cell formed by the base station 91 to another cell, the mobile terminal 92 again moves into the cell formed by the base station 91. Furthermore, it is assumed that a cell ID and a “Value tag” are contained in the SIB1.
The mobile terminal 92 retains received notification information as history information even after the mobile terminal 92 moves from one cell to another cell. When the mobile terminal 92 again moves into the cell formed by the base station 91, the mobile terminal 92 receives, from among notification information transmitted from the base station 91, the SIB1 that contains a cell ID and a “Value tag”. Then, the mobile terminal 92 determines whether the cell ID contained in the SIB1 matches the cell ID contained in the notification information retained in the mobile terminal 92. If both cell IDs match, the mobile terminal 92 compares the “Value tag” contained in the SIB1 received from the base station 91 with the “Value tag” of the notification information retained in the mobile terminal 92.
If the cell IDs differ or if the “Value tags” differ, the mobile terminal 92 receives all the pieces of notification information transmitted from the base station 91. Then, the mobile terminal 92 updates all the pieces of notification information retained in the mobile terminal 92 to the notification information received from the base station 91.
As described above, when the mobile terminal 92 moves between cells, the mobile terminal 92 may sometimes receive all the pieces of notification information transmitted from the base station 91. Accordingly, as illustrated in the lower portion of FIG. 19, the mobile terminal 92 consumes received electrical power when it receives the SIB1 to the SIB11. Accordingly, in the mobile terminal 92, the electrical power consumed when the receiving process is performed on the notification information increases. The mobile terminal 92 also receives the SIB1 when the power supply of the mobile terminal 92 is turned on or when the mobile terminal 92 moves into a service range from outside a service range. At this time, if cell IDs or “Value tags” differ, the mobile terminal 92 receives all the pieces of notification information. Accordingly, when the power supply of the mobile terminal 92 is turned on or when the mobile terminal 92 moves into a service range from outside a service range, the electrical power consumed when the receiving process is performed on the notification information also increases.